The present invention relates to the forming of materials by extrusion.
In a known extrusion process the force of extrusion of a material, which material can be a metal feedstock, through a die means is derived by maintaining frictional engagement of the material with passageway defining surfaces of a member which is moved towards the die means such that frictional drag of the passageway defining surfaces urges the material through the die means.
Thus it is known to provide an extrusion apparatus having first and second members defining an elongate passageway therebetween, the first and second members being movable one relative to the other in the direction of the length of the passageway, an abutment member fixed relative to said second member to project into and block the passageway, means defining at least one die orifice leading from the passageway and associated with the abutment member, means for continuously feeding material into the passageway at a point spaced from the abutment member, the amount of surface area of the passageway defined by the first member which is movable towards the abutment member being greater than the amount of the surface area of the passageway defined by the second member whereby material fed into the passageway is moved by frictional drag with the surface of the passageway in the first member towards the abutment member and is thereby extruded through the die orifice or die orifices.
Conveniently the first member can be a wheel member having an endless groove therein with the second member covering a part of the length of the groove to form the passageway. The abutment member, which can be integral with the second member or formed as a separate component, projects into the groove to block one end of the passageway. The second member and the abutment member are held stationary and the wheel member is rotatable to drag material supplied to the end of the passageway remote from the abutment member along the groove towards the abutment member for extrusion through the die orifice or orifices.
The material fed into the passageway is carried towards the abutment member and extruded through the die orifice or orifices by the frictional drag produced at the surface area of the passageway defined by the movable member. The passageway can have a rectangular section with three walls thereof formed by the two side walls and the base of the groove in the movable member and the fourth wall being defined by the undersurface of the stationary member. The three walls in the movable member urge the material by frictional drag towards the abutment member while the material slides over the fourth wall formed by the undersurface of the stationary member. If the frictional coefficients are the same for all four walls and since the stationary surface is opposing the frictional drag applied to the material by the base of the groove in the movable member, in effect the material is carried towards the abutment member and extruded through the die orifice or orifices by the frictional drag of the two side walls in the movable member.